This invention relates to an improved coupling between the downwardly inclined forward or rearward end of a truck-mounted concrete mixer drum and the output of the gear train of a power transmission apparatus mounted on the truck for rotatably driving the drum.
It is known to journal one end of a mixer drum on the housing of a rotary power transmission by means of a spherical type bearing thereby to accommodate axial misalignment between the drum and transmission due to deflection of the truck frame upon which these massive devices are mounted. Prior patents to Jaeger U.S. Pat. No. 2,563,336; Gerst U.S. Pat. No. 2,732,189; Funk U.S. Pat. No. 3,658,303; and Ries U.S. Pat. No. 3,912,239 show this use of a spherical bearing in a mixer drum and transmission combination.
While provision of spherical type journals for the drum allows limited oscillatory and nutational movement between the drum and the transmission housing, additional means must be provided to couple efficiently the torque of the transmission to the drum even under maximum conditions of misalignment between their respective rotational axes; otherwise, the gears and bearings of the transmission will be subject to severe strain and resultant excessive wear and possible damage. This objective has been realized to some extent by providing a transmission output gear wheel which imparts rotary driving force to a meshing gear attached to the drum as shown in prior patents to Mikulowicz U.S. Pat. No. 3,851,862 and Mann et al. U.S. Pat. No. 4,006,946. These prior art devices employ spherical journals for the drum-to-transmission mounting and have arcuate gear teeth formed on the output coupling gear. In both prior art devices the drive coupling gears are necessarily greater in diameter than the spherical bearing and the gear bodies are specially configured to locate the outer rim thereof in radially surrounding relation with the bearing whereby the longitudinal center points of the arcuate teeth lie in a plane which contains the center of the spherical bearing.
While the aforedescribed prior art devices are capable of torque transmission under conditions of misalignment, the use of known output drive gears in this application entails a specialized gear wheel configuration of substantial diameter. Moreover, the gear teeth must be not only great enough in number and size to withstand high unit driving pressure, but the arcuate drive surface area of the teeth must have a longitudinal dimension across the rim of the gear great enough to provide adequate driving contact over the full range of tooth misalignment permitted by the spherical bearing. As the size and weight of mixer trucks and drums increases, the flexure of the structural members of the truck frame, hence the potential for drum-to-transmission misalignment, increases accordingly. Moreover, the torque required to effect drum rotation has increased as larger payloads are carried by mixer trucks. To those skilled in the art, it will be apparent that under such conditions of increased potential for misalignment and greater torque, a wheel-type gear coupling between the drum and the transmission would have to be altered in size or strength, or perhaps both, to provide enough usable tooth engagement surface to withstand higher unit loading along with greater misalignment between meshing teeth. From the standpoint of weight, compactness and cost, it is undesirable to upgrade the torque transmitting and misalignment tolerance characteristics of such already bulky output gear couplings by the simple expedient of further enlargement and strengthening.